The present invention relates to a piston-type compressor and, in particular, to a piston-type compressor including a piston arranged to reciprocate within a cylinder bore of a cylinder block.
Reciprocating compressors of the type disclosed in, for example, Japanese Laid-Open Patent Publication No. 6-117365 have been conventionally known as a piston-type compressor. The reciprocating compressor disclosed in the above-described publication includes a cylinder block having multiple bores around the axis, a drive shaft borne in a shaft hole of the cylinder block, and multiple pistons linked with a swash plate in a crank chamber that cooperates with the drive shaft and arranged to move linearly within the corresponding bores. Communication passages are formed between the respective bores and the shaft hole to provide communication there between. The drive shaft is coupled in a synchronously rotational manner with a rotary valve. The rotary valve has a suction passage for sequentially providing communication between the communication passage of the respective bore in which a suction stroke is being executed and a suction chamber. The rotary valve includes a residual gas bypass passage. The residual gas bypass passage includes a high-pressure opening portion, a low-pressure opening portion, and a communication path. The high-pressure opening portion provides communication via the bore on discharge termination and the corresponding communication passage. The low-pressure opening portion provides communication via the bore in which compression work is substantially ongoing in synchronization with the discharge termination and the corresponding communication passage. The communication path connects the high-pressure opening portion and the low-pressure opening portion. Specifically, a residual gas bypass groove is formed as the residual gas bypass passage within a seal region opposed to the communication passage of the respective bore in which a compression and discharge stroke are being executed, on the outer peripheral surface of the rotary valve.
In the reciprocating compressor disclosed in the above-described publication, by rotating the rotary valve in synchronization with the drive shaft, refrigerant gas in the suction chamber is sequentially taken into the respective bores through the suction passage of the rotary valve and the communication passage of each bore in which a suction stroke is being executed. The operation of taking the refrigerant gas into the respective bores is then continued smoothly and stably, and therefore the pressure loss becomes significantly low.
Also, by rotating the rotary valve in synchronization with the drive shaft, residual gas within the bore on discharge termination is recovered through the high-pressure opening portion and transferred through the communication path to the low-pressure opening portion. Since the completely compressed refrigerant gas is conducted into the bore in which a compression stroke is being executed without depressurization at a suction pressure, unnecessary recompression can be reduced, the operation runs under a relatively sufficient power efficiency. Further, since the residual gas is less likely to re-expand during a suction stroke of the bore, the refrigerant gas in the suction chamber is reliably taken into the bore.
Piston-type compressors of the type disclosed in, for example, Japanese Published Laid-Open Patent Publication No. 5-71467 have been proposed as another conventional technique. In the piston-type compressor disclosed in the above-described publication, communication grooves are formed to radially provide communication between respective cylinder bores and a valve chamber in which a rotary valve is housed. The rotary valve housed in the valve chamber is coupled in a synchronously rotational manner with a drive shaft. The rotary valve is formed with a suction gas passage and a suction gas guide groove for sequentially providing communication between the communication groove of the respective cylinder bore in which a suction stroke is being executed and a suction chamber. Inside the rotary valve, a gas release hole for conducting residual gas from the cylinder bore on discharge termination to the low-pressure cylinder bore is formed in a manner penetrating in the radial direction of the rotary valve.
In the piston-type compressor disclosed in the above-described publication, with a relative rotation between the cylinder block and the rotary valve in conjunction with the reciprocation of the respective pistons, the gas release hole of the rotary valve provides communication between the compression chamber of the cylinder bore in which the discharge of compression gas has been completed and the compression chamber of the other cylinder bore in which the suction of compression gas has already been completed at the completion of discharge of the former cylinder bore. This causes high-pressure residual gas in the compression chamber of the cylinder bore in which discharge has been completed to be released into the compression chamber of the other cylinder bore in which the suction of compression gas has already been completed and thereby the pressure in the compression chamber of the cylinder bore in which discharge was completed to be reduced. Accordingly, even when the piston of the cylinder bore starts a suction stroke, the re-expansion volume of the residual gas in the compression chamber is significantly low and the gas intake into the compression chamber is swiftly started.
In the reciprocating compressor disclosed in Japanese Laid-Open Patent Publication No. 6-117365, however, since the residual gas bypass groove is formed in the outer peripheral surface of the rotary valve, refrigerant gas is likely to leak through the boundary between the cylinder block and the rotary valve. There has thus been a demand to prevent leakage of refrigerant gas more reliably. Further, the residual gas bypass groove, which is provided along the outer peripheral surface of the rotary valve, is difficult to machine and form. This may result in poor productivity. In addition, the depth of the groove is subject to dimensional constraints in consideration of various conditions such as strength.
In the piston-type compressor disclosed in Japanese Laid-Open Patent Publication No. 5-71467, since the gas release hole is formed in a manner extending through in the radial direction of the rotary valve, only one time of hole machining is required to form the gas release hole, which is easier than machining a groove in the outer peripheral surface. However, if an axial communication hole, for example, is formed at the center of the drive shaft to provide a recovery passage for recovering oil there through, it is difficult to provide a through-type gas release hole in the hollow drive shaft. Although the gas release hole may be formed around the communication hole formed in the drive shaft, not only does hole machining become troublesome involving complications such as being required multiple times, but also an advanced hole machining technique may be required.